Abstract:
In this paper, we assess the hazard of heavy metal pollution of soil in the Vidinska Lowland (Bulgaria) in the case of inundation from the Danube. The assessment takes into account the following two parameters: degree of heavy metal pollution of river sediment (Ме) and topography (To). Each parameter is characterized by the following elements: weight (W), ranges, and ratings (R). Each parameter is evaluated by comparison with the others to determine its relative importance. The highest weight is given to the indicator ‘degree of heavy metal pollution of river sediment’ followed by the ‘topography’. Their weight coefficients are 2 and 1, respectively. The ranges of the parameters characterize the variety of environmental settings throughout the wetlands for the accumulation of heavy metals in the soils of the floodplain. Ratings (R) from 1 to 4 is assigned to each of the ranges of the individual variables. The MeTo index is calculated as the sum of the products of ratings (R) and weights (W) assigned to each of the parameters: MeTo=МеW*MeR+ToW*ToR. The minimum value of the MeTo index is 3 and the maximum is 12. The whole range is divided into six classes: 3 (negligible hazard), 4-5 (very low hazard), 6-7 (low hazard), 8-9 (moderate hazard), 10-11 (high hazard), and 12 (very high). Degree of heavy metal pollution of river sediment (Me). To elaborate on the raster file of the river sediment contamination, we used data on the concentration of As, Cu, Zn, Pb, Cr, and Ni in one representative sample of Danube overbank sediment deposited in the Vidinska Lowland. The index Cd is calculated to be 1.53 for the Danube overbank sediment in the lowland. This value falls in the range 1-3 of the index and is rated to 3. То delineate the limits of the lowland and the geomorphographic landforms, we extracted the slope, aspect, and hillshade from the DTM using the Spatial Analyst Tools – Surface in ArcGIS. The categories of the geomorphographic units are defined according to the classification of Mishev (1959) and Tcherkezova (2019). After classifying and analysing these indicators and comparing them with topographic maps, the following geomorphographic units are defined: low floodplain, high floodplain, and sandy ridges. The calculated values of the MeTo index for the Vidinska Lowland are within the range 3-6 and fall into two classes of a hazard: negligible hazard (26.51% of total area) and low hazard (73,49% % of total area).